In recent years, in order to reduce environmental load, a power generation system utilizing natural energy such as solar power generation, that does not emit carbon dioxide is spreading into homes. Upon power outage, such a power generation system can output the maximum power of 1500 W from a self-sustained operation outlet provided therein in advance.
In addition, in order to cope with power shortage or the like after Great East Japan Earthquake, a system having a storage battery, a system using an electric automobile as a storage battery, a system combining solar power generation and a storage battery, and the like are being developed.
For example, a conventional power feed system includes a first power receiving section 1 connected to a solar battery, a second power receiving section 2 connected to a storage battery, a first DC/DC converter 11 for transforming output voltage of the first power receiving section 1, and a second DC/DC converter 12 for transforming output voltage of the second power receiving section 2, and sets a difference between output voltages of the first and second DC/DC converters, thereby setting priority on the solar battery or the storage battery. In the case of power outage, output voltage of the second DC/DC converter 12 is set to be lower than output voltage of the first DC/DC converter 11, whereby power from the solar battery is preferentially supplied to a load (see, for example, Patent Document 1).